Voltage and current regulation



Feb. 10, 1953 J. A, POTTER 2,628,340

l VOLTAGE AND CURRENT REGULATION Filed July 29, 1947 3 Sheets-Sheet l BVA POTTER ALTURA/E V Feb. 10, 1953 J. A. POTTER 2,628,340

VOLTAGE AND CURRENT REGULATION Filed July 29, 1947 5 sheets-sheet 2/NVENTOR By' J. A. POTTER A TTORNEV Feb. 10, 1953 J, A, POTTER VOLTAGEAND CURRENT REGULATION Filed July 29, 1947 3 Sheets-Sheet 3 /NVE/vrof?J.. POTTER By ATTORNEY Patented Feb. 10, 1953 UNITED STATES PATENTOFFICE VOLTAGE AND CURRENT REGULATION Application `l'uly 29, 1947,Serial No. 764,49)

11 Claims.

This invention relates to current and voltage regulation andparticularly to regulated rectifying apparatus for supplying directcurrent to a load circuit comprising a battery connected across a load.

An object of the invention is to provide iinproved apparatus forminimizing voltage changes across a load to which current is suppliedfrom a current source.

Another object is to provide apparatus for regulating the currentsupplied to a load to minimize load voltage changes and, when thecurrent required for constant load voltage is excessive, for regulatingthe current supplied to the load to minimize load current changes.

A further object is to provide apparatus responsive to the relativemagnitudes of a iirst and a second space current for controlling a thirdspace current in accordance with the amplitude of one only of said rstand second space cur rents.

Another object is to provide apparatus for controlling the currentsupplied to a load under control of a charge on a condenser which ischanged in one direction when the load voltage is greater than an upperlimiting value and in the opposite direction when the load voltage isless than a lower limiting value.

Another object is to provide for controlling a voltage responsive deviceimproved apparatus comprising a plurality of resistors and a pluralityof varistors.

ln a specific illustrative embodiment of the invention herein shown anddescribed, there is provided a three-phase bridge rectier to whichcurrent from a three-phase alternating current source is suppliedthrough transformers for supplying direct current to a load circuitcornprising a battery. The secondary transformer windings aredelta-connected and the primary windings are connected in pathsrespectively which are delta-connected. Three saturable reactors areconnected in series with the primary windings respectively, thereactances of the saturable reactors being varied under control ofcurrent supplied to saturating windings of the saturable reactors tocontrol the voltages across the transformers, respectively, and therebythe rectified current supplied to the load circuit.

Current is supplied to the satura-ting windings f from an auxiliaryrectier through the space current path of a space current device orseries regulator tube. The resistance of the space current path of theseries regulator tube is controlled by controlling the potential of itscontrol electrode with respect to its cathode potential to therebycontrol the current supplied to the saturating windings..

in one of two alternative arrangements for controlling the currentsupplied to the saturating windings of the saturable reactors, acondenser connected in the control grid-cathode circuit of a seriesregulator tube is quickly charged from a direct current source when thecircuit is started in operation to maintain at a low amplitude thecurrent supplied from a space current rectifier to the saturatingwindings so as to avoid damaging the iilamentary cathode of the rectiertube during an initial period while it is being heated to operatingtemperature. When the rectier tube cathode has been heated suliiciently,the rectier supplies energizing current to a starting relay whichoperates to open the condenser charging circuit. There are provided asecond relay which is operated when the battery voltage is suiiicientlylow to complete a high time constant discharge current circuit for thecondenser and a third relay which is operated when the battery voltageis sufficiently high to complete a high time constant charging currentcircuit for the condenser. The current supplied through the seriesregulator tube to the saturating windings is thus increased or decreaseddue to the change of charge on the condenser. While the second and thirdrelays are unactuated, the charge on the condenser will remain nearlyconstant for a long period to cause the battery to be charged at anearly constant rate, the condenser being discharged very slowly dueonly to leakage resistance. An excessive battery charging current causesthe operation of a fourth relay which completes an energizing circuitfor the second relay thereby causing the condenser to be charged toeffect a lowering of the battery charging rate.

In the second alternative arrangement for controlling the seriesregulator tube, there are provided two amplifiers having a common outputstage. The one amplifier is controlled in response to battery voltagechanges to set up a control voltage for a series regulator tube forcausing voltage changes across the battery and load to be minimized. Theother amplifier is controlled in response to changes of current suppliedfrom the battery charging rectifier to the battery and the loadconnected across it to set up a control voltage for the series reguiatortube for causing the battery charging rectifier to supply current at apreselected, substantially constant rate. Means are provided forautomatically making effective for controlling the battery chargingcurrent either the voltage regulating amplifier or the currentregulating amplier whichever at the time requires the smaller current tobe supplied by the battery charging rectier. This means comprises aunidirectional voltage source and in series therewith two parallelbranch paths, the one branch assenzio path comprising an asymmetricalvaristor and in series therewith a portion of the space current circuitof a space current tube in the voltage regulating ampliiier and theother branch path comprising an asymmetrical varistor and in seriestherewith a portion of the space current circuit of a space current tubein the current regulating amplier. One of the varistors is thus madeconducting to cause the completion of a circuit from either the voltageregulating amplier or the current regulating amplier to the inalamplifier stage. Thus, when excessive current is being supplied by thebattery charging rectier under control of the voltage regulatinga-mplier, the voltage regulating amplifier is disconnected from thefinal amplier stage and the current regulating amplifier is connected tothe final amplifier stage to causethe battery charging.v rectifier tosupply a preselected constant current; When, subsequently, the batteryvoltage has increased suiciently, the current regulating anipliner isdisconnected and the voltage regulating amplifier is connected to thenal amplifier stage, and the battery is charged at a lower rate requiredto maintain the voltage across the battery and the load substantiallyconstant.

There is required for the operation or the regulating circuit employingthe amplifying and current regulating space current devices asubstantial-ly constant direct voltage source and a substantiallyconstant alternating Vvoltage source. For supplying the direct voltagethere is provided an auxiliary full wave rectifier to which alternatingcurrent is supplied from a supply line through a transformer, thesecondary windingr of which is connected through a series resistor totheinput terminals of the rectier. A gaslled, cold cathodetube is connectedacross the output terminals of the rectier to maintain the. outputvoltage nearly constant but rising slightly with increasing supply linevoltage. The voltage across the input of the rectifier, therefore, isalso nearly constant but slightly rising with increasing line. voltage,the larger portion of the` voltage changes. which occur across thesecondary' transformer windincr appearing across the. resistor which isconnected in series with the rectifier input. e, substantiallyl constantalternating. voltage is derived by supplying current fromV a portion ofthe secondary trancforrner winding throughV the series resistor to theprimary winding of a second transformer, the portion of the secondarytransformer windingk of the `iirst transformer which is used for thispurposeV being such that alternating voltage changes across it aresubstantially equal to the alternating voltage changes appearing 'acrossthe resistor. The voltage changes across Ythe transformer portion andacross the resistor thus balance each other and the voltage across thesecond` transformer is therefore substantially constant. Y

The invention will now be described in greater detail with reference tothe accompanying drawing, Figs. l to 3 of `which when placed as shown inFig. 4 are a schematic View of a regulated rectifier embodying theinvention.

Referring to the drawing, a three-phase bridge rectier comprisingrselenium rectiiier elements l, is providedv for "supplying chargingcurrent to, a battery H across which is connected a load l2 which-mayvary. Current from the three-phase alternating Vcurrent supply sourcelapis supplied to the rectier it through transformers having primarywindings lll, i5 and it, respectively, and delta-connected secondarywindings il', i3 and i9, respectively. There are provided threesaturable reactors having alternating current windings 2li, 2l and 22,respectively. Reactor Zt has saturating windings 23 and 255, reactor 2ihas saturating windings 2e. and 2l and reactor 22 has saturatingwindings 25 and 28. Three current paths are deltaconnected to thethree-phase current source i3. The one path comprises transformerwinding i@ and reactor winding 2t in series, the second path comprisestransformer' winding l5 and reactor winding 2l in series and the thirdpath comprises transformer winding it and reactor winding 22 in series.The output current of the rectifier it ows ythrough a circuit comprisingin series a resistor Eilfbattery l lfinductance elements 39 and Bl of a,ripple il ter which also comprises shunt condensers 32 and Vand throughthe saturating windings and 25 connected in parallel. An increase ofAthe rectied current supplied rectifier" iiltojitsj load and iiowingthrough saturating windings 23,"21 and 25 lowers the reactance ofreactor windings 2t, 2l and 22, therebypreventing'or minimizing a riseof voltage drop racross reactor' windings it, 2i and 2:2 due to.increased currentiowing therethrough. Switching' means, not shown, arepreferably provided.A for disconnecting 'the battery il and itsloadfromthe. circuit Yof rectifier lf3 when the power source i3. failsor is 'disconnected from the transformer primaryl circuit. ill, l5, it.This switching 'means maybe a relay having a winding connected across',resistorv 2t and is provided for the purposev of preventing the flow ofdischarge current from battery H through the reverse resistance of therectiiier elements it.

Two control circuits are provided for alter.- natively controlling thecurrent suppliedjtosaturating windings 2t, 2'? and. 2e. to'control thereactances ofthe saturable reactors and'thereby to control thealternating voltage impressed upon the rectiier le, the direct-current'supplied by the rectifier' to its loadv including thefha'tteryi i and the load voltage. VWhen switches '3.511 Yand 35 are closed tothe right, as viewed Vinthe drawing, current is supplied to saturatingwindings it, fili/and 2s from an auxiliary rectifier comprising a'rectifier tube it through the space current path of "a, seriesregulating tube a filtering condenser et; being connected across thissupply circuit. This control circuit; isrenergized,l when switch ifivjisclosed, by current supplied to it from alternating current source 39 byway or a transformer having a primary winding it and secondary windingsiii, e2, and t3. Heating ciujrentfor the ifilanientary cathode of tubeSt is supplied from vtiansformer-Ywindine ill- Theend terminals@ iraf,f,ormer1wind ing 42 are connected tothe anodes,l respectively, of tubemend a mideterminal of winding@ du is connected to the 'negativeoutputterminal C of the auxiliary supplycircuit.` The cathode ofrectifier tube 35 is `connected directly to the anode of seriestubeMSl-and through aY resistor te to the screen ridf of tube 3l, thecathode of tube 3i being connectedto the positive out,- put terminal C.A tll-nicrofarad condenser i5 directly connects the control grid-cathodecircuit of tube 37 and a' circuit.. comprising in series Z200-ohmresistor it andtl-microfarad condenser ill also connects the controlAgrid and cathode'of tubeV S7.,

Transformer winding 43 supplies current which is rectified by rectifierelement 48 to 4-microfarad condenser 49 for charging it. The rectifiercomprising tube 35 also supplies current to a circuit comprising16,000-ohm resistors 50 and 5I and 4-microfarad condenser 52 all inseries. The termin-alsof condenser 52 are connected to the winding of astarting relay 53. When switch 44 is closed to start the energization ofthe control circuit, the rectifier circuit comprising rectifier element48 supplies charging current for condenser 41 through the closedcontacts of relay 53. The charging of condenser 41 causes to beimpressed upon the control grid of tube 31 with respect to its cathode anegative biasing potential for increasing the resistance of the spacecurrent path of series tube 31. The current which is supplied fromrectifier 35 is thus limited to a low amplitude during an initialstarting period while the cathode of tube 35 is being heated tooperating temperature, thereby preventing damage to the cathode of tube36. When the cathode of rectifier tube 3S has been heated sufficiently,energizing current is supplied to the winding of relay 59 to cause it tooperate and thereby open the charging circuit for condenser 41.

'Ihere are provided relays 55 and 5S for controlling the charge oncondenser 41 and thereby the current supplied to the saturating windings25, 21 and 28. A voltmeter relay 51, the armature of which is connectedto ground, has its actuating winding connected to the terminals +B and Bof battery II. When the voltage of battery Il is below a certain minimumvalue, the voltmeter relay closes a circuit for energizing the windingof relay 5S by current from battery 59 the negative terminal of which isgrounded. Relay 55 when operated completes a circuit for slowlydischarging condenser 41 through an adjustable resistor 59, the timeconstant of this discharge circuit being of the order of severalminutes. The current supplied to the saturating windings 25, 21 and 28and, therefore, the current supplied from rectier Il) to battery II, isgradn ually increased as the condenser 41 discharges. When the batteryvoltage has increased sufliciently, the voltmeter relay 51 opens theenergizing circuit for relay 56. The current supplied to the saturatingwindings will then remain nearly constant and battery I I will becharged at a nearly constant rate determined by the charge on condenser41 which leaks off at a very slow rate. 1f, subsequently, the voltage ofbattery II exceeds a certain maximum, the voltmeter rela-y 51 willcomplete an energizing circuit for relay 95 which in turn completes acharging circuit from transformer winding 43 and rectifying element 48through resistor 59 to condenser 41. The charge on condenser 41 thusgradually increases to cause a reduction of the energizing currentsupplied to saturating windings 26, 21 and 28 and therefore a reductionof the charging rate of battery I I. Should the current supplied byrectier IIJ to the battery II and load I2 become too high, the overloadrelay G will operate to cause the completion of an energizing circuitfor relay 55, the operation of which causes the current supplied fromrectifier I9 to be reduced. The winding of relay 60 is connected toterminals +B and +R so that the relay winding has im pressed upon it thevoltage drop across resistor 29 which is in series with the chargingcircuit of battery II.

When switches 34 and 35 are closed to the left, as viewed in thedrawing, the saturating windings 26, 21 and 28 in series are suppliedwith current from a rectifier comprising a rectifier tube 10 through thespace current path of a series regulating space current tube 1I, afiltering condenser 12 4being connected across the supply leads going toterminals A and A'. When switch 13 is closed, current from analternating current source 14 is supplied to the primary winding 15 of atransformer having secondary windings 1G and 11 and to the primarywinding 18 of a transformer having a secondary Winding 19. The endterminals of transformer winding 16 are connected to the anodes,respectively, of tube 1s and a mid-tap of this winding is connected tothe negative output terminal A of the regulated rectifier. The cathodeof tube 10 is directly connected to the anode of regulator tube 1I andthrough a resistor 80 to the screen grid of the regulator tube, thecathode of the tube 1I being connected to the positive output terminal Aof the regulatedy rectiiier. A 0.006-microfarad condenser 8I is providedin a path directly connecting the control grid and cathode of tube 1Iand a second path connecting the control grid and cathode of this tubecomprises in series a 0.95- rnicrofarad condenser 82 and a Z200-ohmresistor B3. Transformer winding 11 supplies current through arectifying element 84 to a 4-microfarad condenser 85 for charging it,thereby providing an auxiliary source of direct voltage across conadenser 85.

Alternating current is supplied from the secondary transformer winding19 through a resistor 85 to the input terminals of a bridge rectifier 81the output terminals of which are connected across a load circuitcomprising in parallel a gas-filled, cold cathode tube 88, a filtercondenser 99, a potentiometer 90 and a second potentiometer 9|. The tube88 has the characteristic that the resistance of its space current pathdecreases as the current through it increases so as to mainn tain thevoltage across its terminals nearly constant but rising slightly as thevoltage of source 14 rises. Most of the voltage change which occursacross transformer Winding 19 appears across resistor 86, the voltageacross the input terminals of rectiiier 81 changing relatively little inresponse to voltage changes across transformer winding 19. If, forexample, the voltage across transformer winding 19 rises from 500 to 550volts, the voltage across the input terminals of rectifier 81 may risefrom 170 to 175 volts and the voltage drop across resistor 86 will risefrom 330 to 375 volts, an increase of 45 volts. There is provided atransformer having a primary winding 92 and a secondary winding 93 forsupplying current to the cathode heaters of space current devices aswill be described below. The winding 52 is supplied with current from aportion 943 of transformer winding 19 through a circuit comprisingresistor 89. The transformer portion 34 is selected so that the voltageacross it is larger than the voltage drop across resistor 8s but whichvaries at the same rate as the voltage across resistor 86 with respectto voltage changes of the source 14. If, as assumed above, the voltageacross resistor 86 changes from 330 to 875 volts, the voltage acrosstransformer portion 94 will change from 450 to 495 volts. Therefore, thevoltage across each of the windings of trans- :former 82, 93 will remainsubstantially constant, the voltage across the primary winding 92 beingvolts.

There are provided an ampliiier, called a volt- `age ampliiier herein,comprising a single space Acathode of vtube ii) l.

.current triode I, a second lamplifier, ,called a Vcurrent amplifierherein, comprising two space current triodes lil? and ID3, Ya ,final oroutput amplier stage .comprising a spacecurrent triode iiil andmeanscomprising.asymmetrical varistors ist and It, suchas copper-oxiderectifying elements, for alternatively connecting the Youtput of thevoltage .o1-.current ampliers togtheinput .of kthe iinal lamplifierstage. iVa-ristors are described in anarticle-byJ. lA.,B ecl er in-theJuly 19.40 issue of BellLaboratoriesrRecord on page 322 et seu.While triodes ist, IBI, 1&2 v and v|133 are shown asindividual tubes,l atwin triode tube may be used `instead vci tubes .fltiland III and .atwin triode tube maybeused instead of Itubes H32 and rli, if desired.:Cathode heatingcurrent is supplied to AtubesIliZand-.lB3.from.transformer Q2, 93 and tubes-7l, it and lill maybesimilarly supplied with heating current. The spacecurrent circuit fortube lili maybe traced from the cathode of the tube, througha resistorit to terminal .-B goingto the negative terminal of battery li, `fromthe positive battery terminal through .resistor 2li to terminal +RV,going to the negative terminal of rectier .81, from the positiveterminal of rectier 81 tothe-negative terminal of` the rectifiercomprisingrectier .elementl and from thepositive tern'linal.ofrectiulier 3d through resistorv i'ltc the.anode.oftube lill. Resistor Ili andcondensert acrosswhich the output voltage of rectifier 8d appearsarelconn nected in series in ,the.controlgrid-cathode .cirn Vcuitoiseries vregulatorftube 'ZI softlhat vthe resistance of thes'pacecurrent path o-Ythis tube is controlled inresponse to changes ofVvolta-ge drop across resistor i531. Y

A potentiometer N8 is. connectedacross the terminals -l-B and .-B goingIvo-battery II. rl'he space current circuitof: tube ISB maybetraced fromthe positive .terminal of battery .I i.V through resistor -ES to thenegative terminal-of rectiiier Vel, from thepcsitiveterminarofrectier.87 to minal of battery ii. Whenthe varistor 94 isinthe conducting-or loWresistance-state,the anode-oi tube ill@iseiectivelyconnected tothe A condenser IIIy is V`pro- `vided inV apa-thconnecting the control grid and Vcathode of tube I. Thecontrol grid oftube II is connected through'a--resistor II2 toV the negative outputVterminal of rectifier 84 mso that the dierence of `theyoltage.acrosscondenser 85 and the voltage acrossnresistor Ilisirnpressed upon thegrid with respect to the cathode of tube lill. A ltering condenserIBKyis provided in a path connecting thecontrolgridjandlcathode of tubelili.

'There is-prcvided aebiidge circuit-|29V having resistor l it r`and theVlarger'l portion of potentiometer NBE in-one arm, asymmetricalvaristor'suchthere is connectedacrossthe ttvoterminals/the ,O- f the"dief-fes -Qf battery .H .and iheouiput voltage of -rectier 31. "Theremaining bridge .terminals are connected, respectively,A to the cathodeof tube it@ and ythrough a resistor I2I to the control grid of tube IBB.The vvoltage derived by the bridge circuit IZB andV impressed upon thegridfcathode circuit of tube In!) is the sum of the voltage acrossresistor III] and the .voltage across a portion of potentiometer It? inone arm of the bridge minus the voltage across varistor IIS ina secondarm ofthe bridge. YThe voltage across resistor l it maybe ,about 2,2volts, that across the portion of potentiometer -H38 in the bridgecircuit .about A50 volts and that across vvaristor IIS ,about volts,`making the summation of these .voltages about -2 volts, .'lflegrid ,oftube lili! being negative .with respectto the lcathode. As the voltageof battery Aii increasesfthe voltage across the .bridge .arm .comprising.resistor I Ilandaportion of potentiometer" IFBB increases at Va ,muchhigherratethanthe .rate of increase vol voltagejacross the biridgearm including varistor li, the resistance Vof'varistor I I3 decreasing as thecurrent through it increases. The voltage 'across varistor H3 .is.substantially constant. It varies even less thanthe voltage across theoutput terminals .of rectiiier .855',1the voltage changes appearingmainly across .the resister H5. Thereforalasthe .voltage of. the battery.il increases, the .voltage acrossthe output terminals of the bridgeincreases vto make the control Lgrid of tube iildmorenegative withrespect to its cathode. lf the asymmetrically conducting varistcr its isin the'conductin'g state, the control grid ci tube lill relative to itscathode and the grid of tube I Vrelative toits cathode will each becomemore negative to cause the current supplied to saturating `windings 26,El'and 23 Vof the saturable reactor to decrease and the current suppliedby' rectiiier it .to battery iI to decrease, thereby minimizing theincrease ciabattery voltage. Thegridand cathodeof tube itil areconnected by asecondcircuit which may be traced from the control gridthrough resistors IZB and EQ2-to the posit-ive terminal of rectifier35i, from the negative terminal of rectilier-Sl to the positive.terminal ci .rectifierl 81,"from the negative terminal of rectifier 81'through resistor 2s to thepcsitive terminal of battery Il and from thenegative terminal of 'battery ll through potentiometer H38 and resistor'I I Q to the tube -cathode. As Will be explained below, when thecurrent supplied from rectiiier i!) tothe battery II and its loadincreases, the currentthrough resistor I22 decreases to cause the .gridof tube Iiiii to become less negative with respect to its cathode. Theresult is to increase the voltage supplied to the rectifier Iii When theload on the rectiner is increased, thus compensating fcr'load changes.The resista-nce oi",.varistor lit and therefore thevoltage drop acrossit, tends to decrease with increasing ambienttemperature. To .compensatefor the resistancetemperature `characteristic or varistcr l I3, asuitable ambient temperature responsive resistance Vdevice is'providedin another arm of the bridge. For example, there is provided in theadjacent bridge arnras shown, a directly heated thermistor II?, shuntedby resistor H8, and a series resistor H5. When the ambient temperaturerises,.for example, the Vresistance of thermistcr H1' decreases'toVcause the current through varistcr I I3 to riseandthereby minimize theeffect of ambient temperature changes on the voltage drop acrossvaristrI I3. f llherrnistors lare described in aarticle byGfL.

9, Pearson in Bell Laboratories Record December' 19410 page 106 et seq.

Resistor |3| and condenser |32 in series 'form a resistance-capacityfilter connected across the leads going to terminals A, A. rihere isprovided a current path comprising variable resistor |33, condenser |34and resistor ||2 connected in the grid-cathode circuit of tube 1|, thispath being in parallel with respect to the current path comprisingresistor |01 and the output terminals of rectier 84 across condenser 85.The path |03, |34, ||2 is an anti-hunting or negative feedback pathcoupling the output and input circuits of tube |I. If the control gridof tube |0| is made more negative with respect to its cathode, forexample, the voltage drop across resistor |01 will decrease and currentwill flow in a circuit from the positive terminal of rectiiier 04through resistor |01, condenser for |32, resistor |33, condenser |34 andresistor H2,

all in series, to the negative output terminal of rectifier 04 to changethe charge on condensers in the circuit. The transient voltage set upacross resistor H2, as a result, is in a direction to oppose thepotential change on the grid of tube |0| and the duration of thetransient is determined by the time constant of the resistance-capacitycircuit. The time constant of the circuit may be varied by adjusting thevariable resistor |33 to make the speed of response o the regulatorsystem to changes of current supplied by rectifier I0 as high aspossible while avoiding the setting up of oscillations in the system orhunting.

The space current circuit for amplifier tube r |03 may be traced fromthe positive terminal of battery through resistor 29 to the negativeterminal of rectier 01, from the positive terminal of rectier S1 to thenegative terminal of rectifier 84, from the positive terminal ofrectifier 84 through resistor |22 to the anode of tube |03, from thecathode of this tube to the anode of tube |02 and from the cathode oftube |02 through resistor |23 to the negative terminal of battery Il. Acondenser |44 is in a path connecting the control grid and cathode oftube |02. The anode current circuit of tube |02 may be traced from thepositive terminal of battery through resistor to the negative terminalof rectifier 81 from the positive terminal of rectir;

er 81 through resistor |25 to the anode of tube |02 and from the cathodeof tube |02 through resistor |23 to the negative terminal of battery lThe control grid-cathode circuit of tube |02 may be traced from the gridthrough resistor 20 to terminal +B, through resistor 20, through aportion or" potentiometer 00 and through resistor |21 to the cathode ofthe tube. Thus voltage variations across resistor 29 which areproportional to amplitude variations of the current supplied fromrectifier I0 to the battery and its load 12 are impressed upon thegrid-cathode circuit of tube |02 to control the space current of thetube flowing through resistor |25. The resistor and a portion ofpotentiometer 0| are in the control grid-cathode circuit of tube |03 sothat voltage variations across resistor |25 cause the space current oftube |03 flowing through resistor |22 to change. When varistor |05 is inthe conducting state, the anode of tube |03 is effectively connected tothe cathode of tube |0| so that a voltage equal to the difference of thevoltage across resistor |22 and the voltage of rectiiier 04 set upacross condenser is impressed upon the grid-cathode circuit of tube |0|.When the current amplier comprising tubes |02 and 03 is eiective, thatis when varistor |05 is in the conducting state, if the current suppliedby rectier |0 to battery and its load should rise, 'for example, thevoltage drop across resistor 20 will rise to make the grid of tube |02more negative with respect to its cathode. As a result the grids oftubes 03, |0| and 1| each become more negative with respect to theirrespective cathodes to cause the current supplied to saturating windings20, 21 and 20 to decrease and the rise of current supplied by rectifierl0 to the circuit of battery is thus minimized. The battery chargingcurrent supplied by rectier I0 may thus be maintained substantiallyconstant at an amplitude which may be changed by adjusting thepotentiometer S0. Resistors H0 and ||0 are also connected in a circuitconnecting the control grid and cathode of tube |02, this circuitincluding resistors |20 and |21. If the battery voltage is increased,while the current amplifier is eiective, the voltage drop acrossresistors ||0 and l0 will decrease to make the control grid of tube 02less negative with respect to its cathode. The voltage supplied to therectier i0 is thus increased to compensate for the increased batteryvoltage.

It will be noted that the control grid-cathode circuit of ltube |0|comprises in series resistor ||2, the source of biasing voltageappearing across condenser 05 and two parallel branch paths one of whichcomprises resistor |00 and varistor |04 in series and the other of whichcomprises resistor |212 and varistor |05 in series` When the currentsupplied by rectifier |0 to the battery circuit is less than apredetermined maximum amplitude, the space current of tube |03 flowingthrough resistor |22 will be larger than the space current of tube |00flowing through resistor |09. For this condition the voltage drop acrossresistor |22 will be larger than the voltage drop across resistor |09and the diierence voltage will cause current to flow in the localcircuit comprising resistors |22 and |09 and varistors |04 and |05 allin series. This current flow in the local circuit will be in the lowresistance direction of varistor |04 and in the high resistancedirection of varistor |05. The voltage drop across varistor |04 beingsmall compared with that across resistor |09, the voltage variationsappearing across the resistor |00, rather than the variations acrossresistor |22, are effective in controlling the space current of tube |0Under this condition, then, the charging rate of battery is controlledto minimize battery voltage changes. However, if due to an increase vofload, for example, the current supplied by rectifier |0 to the batterycircuit should increase to the predetermined maximum amplitude, thespace current of tube |03 flowing through resistor |22 will decrease tosuch an extent that the voltage drop across resistor |09 is greater thanthe voltage drop across resistor |22. In this casevcurrent will ow inthe local circuit formed by the two parallel branch paths in the lowresistance direction of varistor |05 and in the high resistancedirection of varistor |04. Therefore the voltage variations appearingacross resistor 22 are effective in controlling the space current oftube |0|. Under this condition substantially constant current issupplied by rectier |0 tothe battery and its load as determined by thesettings of potentiometers and 0|.

Whati's claimed is:

1; In combination, a transformer having a1 primary Windingfto Whichcurrent'may be sup'- plied from an alternating? current supplyy sourceand asecondary winding; aV full Wave reotier'for rectifying alternatingcurrent supplied thereto and-for supplying the rectied current from itsoutput to a direct current load circuit, means for Supplying alternatingcurrent from said secondary` Winding through a series resistor to saidyrectifier,V means connected across said direct current load circuit-atthe output of said recti-A fier having a characteristic that itsresistance decreases as the. current'fiowing through it increasesso asto tend to maintain constant the voltage across said direct current loadcircuit, an alternating current: loadcircuit and means for supplyingalternating current from a portion of said secondaryy Winding throughsaid resistor to said alternating current load circuit, therebymaintaining: substantially constant the voltage across said alternatingcurrent load circuit.

2.. A combination in accordance with claim l in which said portion ofYsaid secondary winding is such that the voltage across it is larger thanthe voltage across said resistor and that the rate of change of voltageacross said portion with respect to supply voltage change issubstantially equal to the rate of change of voltage across-saidresistor' with respecttov supply' Voltage change over the operatingrange of supply'voltage variation.

3. In combination WithV means for supplying current from a currentsupply source to a load,

of a spacecurrent device having an anode, a cathode-and a controlelectrode, means for connecting the anode-cathode path ofvv saidl devicein series Withsaid load with respecttosad source,

a` current path comprising a condenser: coni necting said controlelectrodeand said cathode, a resistor, a source of direct current, anrst switching means for completing' a charging circuit for saidcondenser, said circuit comprising said condenser, said resistor andsaid direct current source all in series, a second switching'means forcompleting a discharging circuit for said condenser, said dischargingcircuit" comprising said condenser and said resistor in series, meansfor operating said rst switching means for causing the current suppliedto the load. to decrease and means for' operating the second switchingmeans for causing the currentl supplied. to the. loadl to increase, thecurrent supplied to the load being maintained relatively steady undercontrol of the: voltage across the condenser! during relatively longperiods when neither switching means is operative.

4. In combination, a saturable reactor having an alternating currentWinding and a saturating winding towhich direct current may be suppliedfor controlling? the reactance of said alternating current Winding, aspace current devicehaving an anode, a cathode and a control electrode,a direct current source, means for supplying current from said directcurrent sourcey to said saturating Winding. through the anode-cathodepath of said space current device, a current path comprising a condenserconnecting said control electrode and said cathoder a source of chargingcurrent for said condenser, relay means responsive to energizing currentsupplied thereto for completing a circuit for charging' said condenserby current from said source of charging current and a second relay meansresponsive toenergizthirdand. a fourth' space current de yhaving ananode, .a cathode a control elec- 1,2'. ing` current suppliedy thereto.for' alternatively. completing a discharge` circuit. for; said.condenser only When saidfirst relayfmeansis unenergized,

thereby controlling." the reactrnce` of said sat-1 urable reactor.

5. In combination). a reotiner; for. rectiiying' currentl suppliedVthereto and for.' supplying the rectifiedr current to a` load, a;saturable reactor having anV alternating: current: windingv and asaturating Winding; for controlling theLreactance of' the alternatingcurrent Winding'. under control of current'- supplied toi the saturatingwinding, meansffor supplying currentfroman alternating current source tosaid'lrectiiier.- through a circuit comprising said alternating currentWinding, a space current'd'evi'ce comprising an anode, a cathode andV acon-trol electrode, means' for supplying direct currentto said?saturating winding through the anode-cathode path. of; said. spacecurrent device, a condenser in .a path connectingsaid controlelectrode'ands'aid cathodera sourceof charging current for saidcondenser, and means for con-trolling the amplituderoi." the rectifiedcurrent supplied to saidload comprising a nrt means for causing' theVcompletionofa circuit for charging said condenser by current. from saidsource of charging current,Y ai' secondv means. for causingvthecompleation` or a. circuit; for discharging said condenser and meansresponsive-to the energization cfs-aid load circuit; for controllingsaid firstl and secondmeans.

6. The combination with: aspacez currentdevice having electrodescomprising anode .and a thermionic cathode of a rectifier!for-converting alternating. current into direct. current, a resistor, anrst transformer having a, primary winding adapted to be conneotedl to.a; source; of alternatu ing current and? asecondary winding, means forsupplying current'v from said secondary winding through said resistorand', through said rectiner in series to ,the space current pathseparating said anode in said cathode, asecondtransforrner having aprimaryf and a secondary Winding, a current'path connected' vacross a-portion of the secondary Winding'of saidrst transformer comprising in`series-saidresi'stor andthe primary Winding of said second transformerand means for supplying' heatingY current. for said thermioniccathode-from thel secondary Winding of said second transiermerr.V

7. In combination, amain. rectier for rectifying alternating currentsupplied. thereto from an alternating-current supplyA source and for supplying the ifectiedcurrentto said load, variable impedance means forcontrolling the alternating current' supplied from. said. source. tosaid rectiii'er, an auxiliary recti'er' for rectify/ing aiternat ingcurrent from' said supply source, a rst space current device. havingananoda a cathode and a control electrode, means for supplying rectinedcurrent from said auxiliary rectifier through the space current path of.said nrst. space current device to said variable impedance means to conutrai its impedance, means' comprising second, vice each trede, aspaceeurrent circuit for' each of ond, third and fourth space current-.parallel branch paths, one o said branch paths vcomprising in. series`a portion of the space cui conducting device, means for impressing upona circuit connecting the control electrode and cathode of said secondspace current device a voltage for causing the current in its spacecurrent path to vary in accordance with load voltage changes, means forimpressing upon a circuit connecting the control electrode and cathodeof said third space current device .a voltage for causing the current inits space current path to vary in accordance with load current changes.a circuit connecting the control electrode and cathode of said fourthspace current device including said two parallel branch paths and meansfor -deriving from the space current path of said fourth space currentdevice and impressing upon the control electrode with respect to thecathode of said first space current device a potential for controllingthe resistance of the space current path of said rst space currentdevice.

8. In combination, a rectier for rectifying current sup-plied theretofrom an alternatingcurrent supply source and for supplying the rectifiedcurrent to a load, a saturable reactor having a core and on said core analternating-current winding the reactance of which may be controlled forcontrolling the current supplied from said source to said rectier, saidreactor having on said core two saturating windings to which directcurrents are supplied for setting up aiding unidirectional magnetomotiveforces in said core, means for connecting one of said saturatingwindings in series with said load so that the rectiiied load currentilows through said saturating winding, an auxiliary rectier forrectifying current from said supply source, a space current devicehaving a space current path and control means for controlling theresistance of said space current path, means for supplying current fromsaid auxiliary rectier through said space current .path to the secondsaturating winding, space current amplifying means for setting up aunidirectional voltage having variations corresponding to load voltagechanges when the load current is less than a certain value and havingvariations corresponding to load current changes when the load currenthas .an amplitude greater than said certain value, and means forimpressing said unidirectional voltage upon said control means tocontrol the resistance of said s-pace curren-t path.

9. In combination, a rst and a second space current device having afirst and a second space current path, respectively, a rst and a secondresistor, means for supplying current to said rst space current paththrough said first resistor to set up a first unidirectional voltageacross said first resistor, means for supplying current to said secondspace current path through said second resistor to set up a secondunidirectional voltage across said second resistor, means for supplyingcurrent from a current source to a load, means responsive to the voltageacross said load for controlling the resistance of said iirst spacecurrent path to thereby control said rst unidirectional voltage, meansresponsive to the current supplied to the load for controlling theresistance of said second space current path to thereby control saidsecond unidirectional voltage, and means responsive to that one only ofsaid first and second unidirectional voltages which differs in amplitudefrom the other of said rst and second unidirectional voltages in apredetermined sense for controlling the supply of current to the load.

10. In combination, a three-phase rectier for rectifying alternatingcurrent supplied thereto and for supplying the rectified current to aload, three transformers having primary windings connected to a supplysource of three-phase alternating current and secondary windingsconnected to said rectier, three saturable reactors each having analternating current winding and a iirst and a second saturating winding,means for connecting said rst saturating windings in parallel, means forconnecting said parallel connected rst saturating windings in serieswith the load so that an increase of load current reduces the reactanceof said alternating current windings, means for connecting saidalternating current windings of said saturable reactors in series withsaid primary transformer windings respectively, an auxiliary rectier forrectifying current from an alternating current supply source to set up adirect voltage across its output terminals, a space current devicehaving an anode, a cathode and a control electrode, means for connectingthe anode-cathode path of said space current device and said secondsaturating windings of said saturable reactors all in series to saidoutput terminals of said auxiliary rectifier, and means responsive tothe voltage across said load for impressing upon the control electrodewith respect to the cathode of said space current device a potential fordecreasing the resistance of the space current path of said spacecurrent device in response to a decrease of said low voltage and viceversa, thereby controlling the reactance of said saturable reactors tocause load voltage changes to be minimized.

l1. A combination in accordance with claim 10 in which there areprovided a condenser, a resistor, a direct voltage source, meansresponsive to a load voltage change in one sense for cornpleting acircuit for supplying current from said direct voltage source throughsaid resistor to said condenser, means responsive to a load voltagechange in the opposite direction for completing a circuit fordischarging said condenser through said resistor, and means forimpressing the voltage to which said condenser is charged upon thecontrol electrode and cathode of said space current device to controlthe resistance of its space current path.

JAMES A. POTTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,650,072 Jonas et al. Nov. 22,1927 1,865,562 Gilson July 5, 1932 1,965,439 Stoller July 3, 19342,005,892 Gulliksen June 25, 1935 2,018,348 Dijksterhuis Oct. 22, 19352,019,352 Livingston Oct. 29, 1935 2,020,961 Quarles Nov. 12, 19352,074,552 Logan Mar. 23, 1937 2,079,500 Foos May 4, 1937 2,084,870Schmidt June 22, 1937 2,179,299 Murcek Nov. 7, 1939 2,306,998 ClaessonDec. 29, 1942 2,322,130 Hedding June 15, 1943 2,377,363 Noble June 5,1945 2,386,548 Fogel Oct. 9, 1945 2,401,096 Paradise et al May 28, 19462,486,154 Hadfield Oct. 25, 1949 2,501,263 Cherry Mar. 21, 19502,503,880 Mah Apr. 11, 1950

